Reign of Fire: With Recent Strides Made in Understanding the Complex Ecological Cycles of Our Rainforests, Scientists Are Now Better Aware of the Severe Effects of Both Climate Change and Creeping Development on Forest Ecosystems. Julian Cribb Reports on a Growing Call for an Urgent Change to Management Thinking and Practice for Rainforest Areas

Reign of Fire: With Recent Strides Made in Understanding the Complex Ecological Cycles of Our Rainforests, Scientists Are Now Better Aware of the Severe Effects of Both Climate Change and Creeping Development on Forest Ecosystems. Julian Cribb Reports on a Growing Call for an Urgent Change to Management Thinking and Practice for Rainforest Areas

Article excerpt

Most devastating of all the foes of the rainforest is fire. Each year through human action, intentional and unintended, fires obliterate huge areas of the world's remaining rainforests.

And, in a subtle interaction which has scientists deeply concerned, global warming is quietly stoking the fires. As the climate warms, El Nino events become more intense and more frequent, bringing with them the droughts which turn moist forests to tinder.

Researchers at the Australian Rainforest CRC have identified a more disturbing signal still. Rainforests are typically vast sponges for the C[O.sub.2] that is driving global warming. Investigations using a flux tower located in lowland tropical rainforest suggest that, under in normal conditions, a hectare of Australian tropical rainforest pulls around 31 kg of carbon out of the atmosphere every day.

But when conditions turn dry, says the CRC's Deputy CEO, Dr Steve Turton of James Cook University, the forest 'flips' and becomes a net carbon emitter, each hectare liberating around 12 kg a day--equal to a small car--as moisture-stressed trees close their stomata and cease to absorb carbon from the air, and the C[O.sub.2]-emitting microbes in the forest litter remain active. Just what this means for global warming is not yet clear but the possibility exists that more frequent droughts will cause the forests to shed more carbon which will, in turn, fuel climate change, leading to further droughts, fires and carbon release.

It is this intimate linkage of forest, atmosphere, biodiversity and human activity that is the focus of Australian rainforest science, as researchers grapple with a vast and complex system. Spurred by the smoke clouds that blanket the ruined forests of Sumatra, Borneo and the Amazon, there is an acute sense that time is running out for us to fully understand what is going on, and what needs to be done if even a fraction of the world's tropical rainforest is to be saved.

Once, fire was largely kept at bay by the forests: their wet microclimate and rapid decomposition of litter left little for fires to work with, Dr Turton says. The great change came about as humans began to drive roads through the forest for logging and clear large areas for farming. Every road was a highway of death, bringing not only logging trucks but also the hot, sere winds that prepared the way for fires.

'When the rainforest is fragmented, it is much more vulnerable to 'edge effects'--drying, invasions of pests and weeds, human activities. The more fragmented it is, the more it dries and the greater the risk of fire" he says. Unlike sclerophyll (fire-tolerant) forest, rainforest trees are notably poor at regenerating after a fire, and those only lightly scorched often die.

On a map, Australia's tropical rainforest appears extensive and intact, covering some 750 000 hectares from Douglas Shire in the north to Hinchinbrook on the central north Queensland coast. (It is estimated that some 210 000 hectares has been cleared since European settlement.) In reality, the remainder is carved through and through with 1427 km of roads and 324 km of powerline clearings, as well as railways, phone lines, gas and water mains, tourist trails and former logging tracks, every one of them an invasion route for fire, weeds, feral animals, diseases, roadkill, noise and other forms of pollution. Roads themselves may directly impact only two per cent of the forest area--but their effects touch up to 20 per cent, Dr Turton warns.

Fracturing the forest and occupying the richest soil is a century of agriculture, to which runaway urban, infrastructure and tourist development is adding its own, more recent, impacts.

Understanding how to maintain a sustainable forest in the face of this battery of assaults, from the local to the global, represents an extraordinary scientific challenge. Fragmentation is already so widespread it seems almost impossible to reverse and the 650 hectares of tropical rainforest that has been restored with great care and labour in recent years seems like a sandcastle set against the tide. …